A transformer is a magnetic device that transfers electric energy from one circuit to another circuit through coils in order to regulate an input voltage to a desired range for powering an electronic device.
FIG. 1 is a schematic exploded view illustrating a conventional transformer. As shown in FIG. 1, the conventional transformer 1 comprises a bobbin 11, a magnetic core assembly 12, a primary winding assembly 13 and at least one pancake winding assembly 14. The primary winding assembly 13 and the pancake winding assembly 14 are disposed around the bobbin 11. The pancake winding assembly 14 is used as a secondary winding assembly. The magnetic core assembly 12 is partially accommodated within a channel 111 of the bobbin. During operations of the transformer, an input voltage is inputted into the primary winding assembly 13, the magnetic core assembly is subject to electromagnetic induction, and a regulated voltage is outputted from the pancake winding assembly 14.
Generally, the pancake winding assembly 14 of the conventional transformer 1 is implemented by one or more copper foil sheets. The bobbin 11 comprises a channel 111, a main body 112, two lateral plates 113 and plural partition plates 114. The two lateral plates 113 are located at two opposite sides of the main body 112. The plural partition plates 114 are disposed on the main body 112. Moreover, an accommodation space 115 is formed between every two partition plates 114 for accommodating the pancake winding assembly 14. The primary winding assembly 13 is wound around a winding accommodation space 116 between the plural partition plates 114 and the main body 112. Since the partition plate 114 has a specified thickness, a portion of the winding space of the bobbin 11 is occupied by the partition plate 114. Under this circumstance, the overall volume of the conventional transformer 1 is large. Moreover, for expanding the bobbin 11, it is necessary to produce a new mold of the bobbin with a corresponding size. Since the expansion of the bobbin 11 increases the fabricating cost of the transformer 1, the expansibility of the bobbin 11 is limited.
Please refer to FIG. 1 again. The pancake winding assembly 14 further comprises two extension parts 141. The primary winding assembly 13 in one winding accommodation space 116 may cross over one of the extension parts 141 to the adjacent winding accommodation space 116. Moreover, the extension part 141 further comprises an indentation 141a for assisting in positioning the fly line of the primary winding assembly 13. However, since the pancake winding assembly 14 is a combination of plural ring-shaped metallic sheets, the arrangement of the extension parts 141 may increase the complexity of forming the pancake winding assembly 14 and result in lot of metal scrap during the fabricating process. Moreover, since pancake winding assembly 14 is produced by welding the plural ring-shaped metallic sheets, the fabricating cost of the pancake winding assembly 14 is very high. Moreover, after the transformer 1 is assembled, the tightness between the primary winding assembly 13, the pancake winding assembly 14, the magnetic core assembly 12 and the bobbin 11 is possibly insufficient. Consequently, the applications of the conventional transformer 1 are limited.